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250 The other diazines are pyrazine ..
Smith and Heathcock provided the first synthetic route for unsymmetrical bissteroidal pyrazines in 1992 (). α-Azidoketone 24 was obtained by α-bromination of 3-cholestanone 23, followed by displacement of the secondary bromide with sodium azide. Treatment of 24 with O-methyl hydroxylamine provided the O-methoxime, which was reduced with triphenylphosphine in aqueous THF to give 2-amino-3-methoxime 25. To prepare a coupling partner, androstanone 26 was converted to enol acetate 27, which was oxidized with dimethyldioxirane to 2β-acetoxy 3-ketone 28. Initial heating at 90 °C of aminomethoxime 25 with 3-ketoacetate 28, followed by heating at 145 °C provided the first unsymmetrical steroidal pyrazine 29, probably via sequential imine formation followed by loss of AcOH and MeOH ().
Beamand, J.A., Price, R.J. & Lake, B.G. (1992) Comparison of the cytotoxicity and effects on peroxisomal and microsomal enzyme activities of some pyrazines in primary rat hepatocyte cultures. ,12,369.
dimethyl pyrazine: FL/FR: 2-methyl ..
Groups of 4-week-old male Wistar rats were given subcutaneous injections of 2,5-dimethylpyrazine at a dose of 10, 30, 70, 100 or 300 mg/kg bw per day, and 6-week-old animals were given 100 or 300 mg/kg bw per day for 2 weeks. No effects were found on plasma concentrations of testosterone or polyamines or on acid phosphatase activity in the prostate of juvenile rats at the two lower doses, but decreased plasma concentrations of testosterone and prostate concentrations of spermine were observed at doses > 100 mg/kg bw per day, and a decreased concentration of spermidine and decreased acid phosphatase activity in the prostate were reported at doses > 70 mg/kg bw per day. However, these effects were not seen after treatment of juvenile rats for 3 or 7 days or in mature rats given 100 or 300 mg/kg bw per day for 2 weeks. The findings suggest that a high dose of 2,5-dimethylpyrazine inhibits the biosynthesis of polyamines and acid phosphatase in the prostate of juvenile rats by decreasing the concentration of circulating testosterone (Yamada et al.,1994).
There are often challenges in synthetic chemistry or radiochemistry to obtain the desired probe once the biochemical and physiological characteristics are optimized. Depending on the imaging modality, the synthetic chemistry requirements may vary considerably. For example, optical probes are challenged to maximize photon yield while minimizing photobleaching. PET probes are challenged by their shorter half-life and dependence on automation to reduce radiation exposure. For a PET imaging agent to succeed, a reliable and efficient method of synthesis that is translatable across radiochemistry facilities must be established. Furthermore, the synthesis method must be amenable to current Good Manufacturing Practice (cGMP) methods with a comprehensive quality assurance program if the probe is to be applied in human subjects.
2,5-dimethyl pyrazine, 123-32-0 - The Good Scents …
Groups of 4-week-old male Wistar rats were given subcutaneous injections of 2,5-dimethylpyrazine at a dose of 10, 30, 70, 100 or 300 mg/kg bw per day, and 6-week-old animals were given 100 or 300 mg/kg bw per day for 2 weeks. No effects were found on plasma concentrations of testosterone or polyamines or on acid phosphatase activity in the prostate of juvenile rats at the two lower doses, but decreased plasma concentrations of testosterone and prostate concentrations of spermine were observed at doses > 100 mg/kg bw per day, and a decreased concentration of spermidine and decreased acid phosphatase activity in the prostate were reported at doses > 70 mg/kg bw per day. However, these effects were not seen after treatment of juvenile rats for 3 or 7 days or in mature rats given 100 or 300 mg/kg bw per day for 2 weeks. The findings suggest that a high dose of 2,5-dimethylpyrazine inhibits the biosynthesis of polyamines and acid phosphatase in the prostate of juvenile rats by decreasing the concentration of circulating testosterone (Yamada et al.,1994).: Male rats received the dimethylpyrazine isomers subcutaneously at a dose of 0, 10, 30, 70, or 100 mg/kg bw per day for 2 weeks. After administration of 2,5-dimethylpyrazine at 100 mg/kg bw per day, the weights of the prostate and seminal vesicles (also at 70 mg/kg bw per day), plasma testosterone concentration, acid phosphatase activity in the prostate, and the fructose content in the seminal vesicles were decreased. The weight of the testis and acid phosphatase activity in this organ and the numbers of spermatozoa in the epididymides were not affected by 2,5-dimethylpyrazine. At this dose, 2,6-dimethylpyrazine affected only the seminal vesicles, while 2,3-dimethylpyrazine had no effect on reproductive or accessory reproductive organs. The authors concluded that 2,5-dimethylpyrazine decreased prostate and seminal vesicle weights by inhibiting testosterone uptake and reducing plasma testosterone concentrations (Yamada et al.,1993).
The South 1 synthesis started with conversion of hecogenin acetate 32 into enone 64 via a modified Dauben protocol (). After ketalization of the C12 carbonyl, enone 64 was stereospecifically reduced to the allylic alcohol, which was then hydrogenated with platinum oxide to give, after ketal deprotection, the saturated alcohol 93. Proximal functionalization of the C18 methyl group of 93 was accomplished via the hypoiodite method of Meystre which provided lactone 94 after chromic acid oxidation. Sequential hydrolysis of the C3 acetate group, silylation of the hydroxyl group, and LiAlH4 reduction of the lactone moiety delivered triol 95.
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2,5-dimethyl pyrazine, 123-32-0 - The Good Scents Company
The synthesis featured production of cephalostatins 7 and 12, and ritterazine K in one pot via in situ reduction of α-azidoketones (18 and 19) to α-aminoketones followed by statistical combination of the α-aminoketones. When a 1:1 mixture of the North 1 and South 7 unit was treated with ethanolic NaHTe in the presence of SiO2 and O2, α-aminoketones produced in situ afforded the expected pyrazines. The reaction provided the protected pyrazines cephalostatin 7 (20), cephalostatin 12 (21), and ritterazine K (22) in 35, 14, and 23% isolated yields, respectively. Individual deprotection of pyrazines (20, 21, and 22) with excess TBAF afforded the first synthetic samples of cephalostatin 7 (5), cephalostatin 12, and ritterazine K, respectively.
What are the mechanism of reaction in preparing pyrazine?
Since the cephalostatins contain spiroketals, the next logical step was to couple a steroid bearing this structural feature. Thus, α-acetoxyketone 30 was prepared by sequential enolate formation, MoOOPh-mediated α-hydroxylation, and acetylation (). Condensation of 30 with α-aminomethoxime 25 under the same conditions furnished spiroketal-containing unsymmetrical pyrazine 31.
What are the mechanism of reaction in preparing pyrazine
As discussed earlier, the composition of the cephalostatin and ritterazine families implies that nature may utilize random coupling of differentiated steroidal α-aminoketones to produce the bissteroidal pyrazines. Jeong's synthesis prepared unsymmetrical cephalostatin 7 and the dimers of its subunits, cephalostatin 12 and ritterazine K, to explore this `pseudocombinatorial' hypothesis ().
preparation of pyrazine reaction-which its ..
Although the yield of pyrazine is low, this protocol provided a breakthrough for the construction of unsymmetrical pyrazines, thereby enabling subsequent efforts to target the North and South segments of cephalostatin with expectation of unification late in the synthesis. Indeed, all synthetic trisdecacyclic analogs are prepared by late-stage pyrazine formation.
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